1. Field of the Invention
The present invention relates to a correction apparatus for an NC lathe equipped with a spindle, at least two tool rests provided so as to be movable in the direction along the axis of the spindle and in the direction perpendicular to the axis of the spindle, feed mechanisms for moving each of the tool rests in the above-mentioned directions, and a feed controller for generating movement target position data regarding each of the tool rests, for numerically controlling the feed mechanisms on the basis of the generated movement target position data and for moving each of the tool rests to its movement target position, the correction apparatus being used to correct the movement target position of each of the tool rests.
2. Description of the Prior Art
An NC lathe comprises a bed, a spindle stock provided on the bed and rotatably supporting a spindle, a Z-axis guide mechanism provided on the bed to guide in the direction (the Z-axis direction) along the axis of the spindle, a saddle guided by the Z-axis guide mechanism so as to be movable in the Z-axis direction, an X-axis guide mechanism provided on the saddle to guide in the direction (the X-axis direction) perpendicular to the axis of the spindle, a tool rest mounted on the saddle and guided by the X-axis guide mechanism so as to be movable in the X-axis direction, a Z-axis feed mechanism for moving the saddle in the Z-axis direction, an X-axis feed mechanism for moving the tool rest in the X-axis direction, a feed controller (numerical controller) for numerically controlling the operations of the X-axis feed mechanism and the Z-axis feed mechanism, and the like.
The numerical control is carrying out on the basis of NC programs having been created in advance. More specifically, the NC programs are analyzed sequentially by the feed controller, and command signals regarding the movement positions and feed speeds of the tool rest are extracted. On the basis of the extracted command signals, movement target position data (operation command signals) is generated. On the basis of the generated operation command signals, the X-axis feed mechanism and the Z-axis feed mechanism are feedback controlled.
The tool rest and the saddle are required to have sufficient rigidity so that machining can be carried out stably. Hence, they have considerable weights. For this reason, when the tool rest and the saddle are moved, the form of the bed is changed by the movement. This changes the positional relationship between the spindle and the tool rest and impairs the rectilinearity of the tool rest in the Z-axis direction and the X-axis direction, thereby lowering machining accuracy.
In order that the rectilinearity of the tool rest is within a predetermined allowable range in the prior art, when the tool rest is moved in the Z-axis direction for example, the X-axis direction position of the tool rest is corrected so that the displacement of the tool rest with respect to the spindle, caused depending on the movement position of the tool rest, can be canceled.
The structure of the NC lathe, however, is not limited to the above-mentioned structure comprising the tool rest, the saddle and the one set of the X-axis feed mechanism and the Z-axis feed mechanism for driving these. An NC lathe comprising a plurality of tool rests and the like is available. In an NC lathe having this kind of structure, when one of the tool rests and the saddle thereof are moved, the positional relationship between the spindle and the other tool rests is changed. This lowers machining accuracy because of a reason similar to that described above.
In the NC lathe comprising the plurality of tool rests and the like in the prior art, when one of the tool rests is moved, the positions of the other tool rests are changed, but no means is taken to correct the changes of the positions. It is thus impossible to improve the machining accuracy of the NC lathe.
Accordingly, the present invention is intended to provide a correction apparatus for an NC lathe equipped with a plurality of tool rests and the like, being capable of correcting the displacement of each tool rest caused by the positional relationship among the tool rests so that the rectilinearity of each tool rest can be raised and so that the machining accuracy of the NC lathe can be improved.
In order to attain the above-mentioned object, the present invention relates to a correction apparatus for an NC lathe equipped with a spindle, at least two tool rests provided so as to be movable in the direction along the axis of the spindle and in the direction perpendicular to the axis of the spindle, feed mechanisms for moving each of the tool rests in the above-mentioned directions, and a feed controller for generating movement target position data regarding each of the tool rests, for numerically controlling the feed mechanisms on the basis of the generated movement target position data and for moving each of the tool rests to its movement target position,
the correction apparatus for correcting the movement target positions of the tool rests, the movement positions of which are numerically controlled on the basis of the movement target position data, comprising:
a correction amount setting section for receiving the movement target position data from the feed controller, for recognizing the position of each of the tool rests in the direction along the axis of the spindle and/or in the direction perpendicular to the axis of the spindle on the basis of the received movement target position data, and for setting correction amounts for canceling the displacements of the other tool rest in the direction along the axis of the spindle and/or in the direction perpendicular to the axis of the spindle caused depending on the position of the one of the tool rests in the direction along the axis of the spindle and/or in the direction perpendicular to the axis of the spindle, and
a correction execution section for correcting the movement target position data for the other tool rest on the basis of the correction amounts having been set by the correction amount setting section.
According to the present invention, the movement target position data for each of at least two tool rests is generated by the feed controller, and each of the feed mechanisms is numerically controlled on the basis of the generated movement target position data. Hence, each of the tool rests is moved to a movement target position in the direction along the axis of the spindle and in the direction perpendicular to the axis of the spindle by the feed mechanisms.
In an NC lathe equipped with a plurality of tool rests as described above, each of the tool rests usually has a considerable weight. For this reason, the form of the bed of the NC lathe is changed as each of the tool rests is moved. Therefore, when one of the tool rests is moved in the direction along the axis of the spindle for example, depending on the movement position thereof, the position of the other tool rest is displaced in the direction along the axis of the spindle or in the direction perpendicular to the axis of the spindle. Similarly, when the other tool rest is moved in the direction along the axis of the spindle, depending on the movement position thereof, the position of the one of the tool rests is displaced in the direction along the axis of the spindle or in the direction perpendicular to the axis of the spindle.
When the displacements of the tool rests are caused as described above, the positional relationship between the spindle and the tool rests is changed. This impairs the rectilinearity of the tool rests in the direction along the axis of the spindle and/or in the direction perpendicular to the axis of the spindle, thereby lowering machining accuracy.
To solve this problem, the correction amount setting section of the present invention sets correction amounts for canceling the displacements of the other tool rest caused in the direction along the axis of the spindle and/or in the direction perpendicular to the axis of the spindle depending on the position of the one of the tool rests in the direction along the axis of the spindle and/or in the direction perpendicular to the axis of the spindle. In addition, the correction execution section of the present invention corrects the movement target position data for the other tool rest on the basis of the correction amounts having been set by the correction amount setting section. As a result, the rectilinearity of each of the tool rests can be within a predetermined allowable range, and machining accuracy can be improved.
In addition, the correction apparatus of the present invention further comprises a correction amount storage section for storing the correction amounts for canceling the displacements of the other tool rest in the direction along the axis of the spindle and/or in the direction perpendicular to the axis of the spindle caused depending on the position of the one of the tool rests in the direction along the axis of the spindle and/or in the direction perpendicular to the axis of the spindle.
The correction amount setting section searches data stored in the correction amount storage section on the basis of the movement target position data regarding each of the tool rests, which is received from the feed controller. Furthermore, the correction amount setting section reads correction amounts corresponding to the positions of the one of the tool rests in the direction along the axis of the spindle and/or in the direction perpendicular to the axis of the spindle, and sets correction amounts for correction execution on the basis of the correction amounts having been read.
As described above, when one of the tool rests is moved in the direction along the axis of the spindle, depending on the movement position thereof, the position of the other tool rest in the direction along the axis of the spindle or in the direction perpendicular to the axis of the spindle is displaced. Similarly, when the other tool rest is moved in the direction along the axis of the spindle, depending on the movement position thereof, the position of the one of the tool rests in the direction along the axis of the spindle or in the direction perpendicular to the axis of the spindle is displaced.
To solve this problem, in the present invention, the one of the tool rests is moved every predetermined interval in the direction along the axis of the spindle for example, and the displacement amount of the other tool rest in the direction along the axis of the spindle or in the direction perpendicular to the axis of the spindle caused depending on each of the movement positions thereof is measured in advance. On the basis of the measured displacement amount, a correction amount for canceling this is set and stored in the correction amount storage section in advance. Furthermore, the correction amount setting section reads the correction amount corresponding to the movement target position of each of the tool rests from the correction amount storage section. On the basis of this, the correction amount setting section sets a correction amount for executing correction. Therefore, the present invention can also have effects similar to those described above.
The displacement amount of the other tool rest in the direction along the axis of the spindle or in the direction perpendicular to the axis of the spindle caused depending on each movement position of the one of the tool rests in the direction perpendicular to the axis of the spindle can also be measured in a way similar to that described above. In addition, a correction amount for canceling this displacement amount can also be set and stored in the correction amount storage section in advance. Furthermore, a correction amount for canceling the displacement amount of the one of the tool rests in the direction along the axis of the spindle or in the direction perpendicular to the axis of the spindle caused depending on each movement position of the other tool rest in the direction along the axis of the spindle or in the direction perpendicular to the axis of the spindle can be set in a way similar to that described above, and can be stored in the correction amount storage section in advance.
Furthermore, when the movement target position of each of the tool rests does not correspond to the movement position at which the displacement amount is measured, the correction amount of the movement target position can be calculated and set by carrying out interpolation or the like on the basis of the correction amounts of the movement positions at which the displacement amounts were measured.